1. Field of the Invention
The present invention relates to a process for the preparation of aminoketones useful as central muscle relaxants. This invention is also concerned with a process for the preparation of intermediates for the aminoketones.
More specifically, the present invention pertains to a process for preparing a compound of the following formula [VI]: ##STR1## by oxidizing a compound of the following formula [I]: ##STR2## to obtain a compound of the following formula [IV]: ##STR3## and then forming the compound of the formula [VI] from the compound of the formula [IV]. The substituents R, R.sub.1, R.sub.2, R.sub.6 and R.sub.7 will be defined herein. Compounds of the formula [VI] are novel compounds and are useful as central muscle relaxants.
2. Description of the Related Art
It is generally known to use a heavy metal such as chromic acid as an oxidizing agent upon preparation of a ketone from a secondary alcohol. Such heavy metals are however noxious from biological and other standpoints, so that their use in the production of pharmaceutical products is not preferred.
Some processes which use an oxidizing agent other than heavy metals have hence been proposed, including the process using sodium hypochlorite and a phase transfer catalyst in combination [Lee, G. A., et al., Tetrahedron Letters, 1641 (1976)] and the process in which calcium hypochlorite is used in the presence of an acidic solvent such as acetic acid [Nwavkwa, S. D., et al., Tetrahedron Letters, 35 (1982)]. These oxidizing processes were however unable to prepare a ketone of the formula [IV] from an alcohol of the formula [I].
As a still further process for preparing an aminoketone from a ketone, it has been known to react the ketone with paraformaldehyde and an amine hydrochloride in the presence of concentrated hydrochloric acid in an alcoholic solvent (Japanese Patent Application Laid-Open No. 119444/1988). In the aminoketone prepared by this process, the amine moiety is however in its hydrochloride form. It is therefore necessary to convert the reaction product to the free aminoketone by neutralizing it with a suitable alkali agent, for example, aqueous ammonia or an aqueous solution of sodium hydroxide. The above process hence cannot avoid inconvenience such as higher production cost and complicated production steps.